This is blog entry originally written in the middle May 2014. I also seem to writing this code every 3 months or so and then I forgot. So I need a trigger to remember exactly how to work Scala Maps and sort the entries by key.
\nLet’s break out the Scala REPL.<\/p>\n
\r\nWelcome to Scala version 2.10.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_51).\r\nType in expressions to have them evaluated.\r\nType :help for more information.\r\n<\/pre>\nWe will create a map of collection of String associated with Integer elements. This data might have come a key value storage or you may have a similar requirement to work with statistical data.<\/p>\n
\r\nscala> val map = Map( "Jane" -> 3, "Peter" -> 10, "Steve" -> 1, "Anna" -> 5, "Megan" -> 15, "Brian" -> 7, "Sally" -> 8 )\r\nmap: scala.collection.immutable.Map[String,Int] = Map(Megan -> 15, Anna -> 5, Jane -> 3, Brian -> 7, Steve -> 1, Sally -> 8, Peter -> 10)\r\n<\/pre>\nIn order to sort the data structure, we then convert the map to list collection of tuples. <\/p>\n
\r\nscala> map.toList\r\nres1: List[(String, Int)] = List((Megan,15), (Anna,5), (Jane,3), (Brian,7), (Steve,1), (Sally,8), (Peter,10))\r\n<\/pre>\nNow we can sort using the tuples. Here is the descending order on the values:<\/p>\n
\r\nscala> map.toList.sortWith( (x,y) => x._2 > y._2 )\r\nres2: List[(String, Int)] = List((Megan,15), (Peter,10), (Sally,8), (Brian,7), (Anna,5), (Jane,3), (Steve,1))\r\n<\/pre>\nHere is the ascending order on the values<\/p>\n
\r\nscala> map.toList.sortWith( (x,y) => x._2 < y._2 )\r\nres3: List[(String, Int)] = List((Steve,1), (Jane,3), (Anna,5), (Brian,7), (Sally,8), (Peter,10), (Megan,15))\r\n<\/pre>\nHere is another tip. Let’s say you need to create a histogram of 100 different product items. You can create this data structure
\nimmutable at the beginning. However, as you are building the statistic, you may prefer to use an mutable collection map instead.<\/p>\n\r\n val buckets = collection.mutable.Map.empty[Int,Int]\r\n buckets ++= (1 to 100).toList.map{ x => (x,0) }.toMap\r\n<\/pre>\nNow in your statistic gathering part, you can write something like this:<\/p>\n
\r\n val keyName: String = ???\r\n val keyIndex: Integer = convertNameToIndex(keyName)\r\n buckets(keyIndex) = buckets.getOrElse(keyIndex, 0) + 1\r\n<\/pre>\nAnd then render the sorted data into a top ten products<\/p>\n
\r\n val sortedProducts = buckets.toList.sortWith{ (x,y) => x._2 > y._2 }\r\n println(sortedProducts.take(10))\r\n<\/pre>\nThat’s all.<\/p>\n","protected":false},"excerpt":{"rendered":"
This is blog entry originally written in the middle May 2014. I also seem to writing this code every 3 months or so and then I forgot. So I need a trigger to remember exactly how to work Scala Maps and sort the entries by key. Let’s break out the Scala REPL. We will create […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[75,40,6],"tags":[],"_links":{"self":[{"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1626"}],"collection":[{"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=1626"}],"version-history":[{"count":4,"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1626\/revisions"}],"predecessor-version":[{"id":1635,"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/posts\/1626\/revisions\/1635"}],"wp:attachment":[{"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=1626"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=1626"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xenonique.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=1626"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}